Why Isn't a Kilogram a Kilogram?

The video discusses the kilogram, the basic unit of mass in the metric system, and its historical development. Initially defined by the weight of water, the kilogram became an international standard in 1875. However, the physical prototype used to define it has become unreliable, with its mass drifting over time. Scientists aim to redefine the kilogram using the Planck constant, a universal constant, to ensure precision. This involves using a Watt balance to measure mass in terms of electric current and voltage. The goal is to establish a new definition by 2018, eliminating the need for physical prototypes.

What was the original basis for the kilogram after the French Revolution?

• The weight of gold

• The weight of grain

• The weight of water

• The weight of air

What material was used to create the prototype kilogram?

• Gold and silver alloy

• Iridium platinum alloy

• Copper and tin alloy

• Steel and aluminum alloy

What issue was discovered with the kilogram standard about 30 years ago?

• The prototype was stolen

• The copies were corroding

• The masses of the original and copies were drifting apart

• The prototype was melting

What is the Planck constant used for in the context of redefining the kilogram?

• To calculate speed

• To determine volume

• To measure temperature

• To relate a photon's energy to its frequency

What device is used to measure an object's weight using electric current and voltage?

• A digital scale

• A beam balance

• A spring scale

• A Watt balance